Knee Pain Severity Tied to Widespread Pain

No significant association with structural damage

Action Points

In patients with or at risk for osteoarthritis, the severity of knee pain and having bilateral symptomatic knee pain was a significant risk factor for incident widespread pain, indicating that localized pain can be involved in the development of widespread pain.

Note that structural pathology independent of pain severity was not significantly associated with increased risk for incident widespread pain, highlighting the importance of pain symptomatology as an important factor that can contribute to the onset of widespread pain.

The severity of localized pain in patients at risk for knee arthritis was associated with the development of widespread pain (WSP), according to Canadian investigators.

In contrast, underlying structural pathology of the knee, independent of pain severity, was not significantly associated with an increased risk of widespread pain, they wrote in Arthritis Care & Research.

Musculoskeletal pain disorders such as knee arthritis can affect joints in isolation, or regionally, or even result in widespread pain throughout multiple parts of the body, while widespread pain is associated with a greater susceptibility to mental disorders, physical disability, cardiovascular risk, and a poorer quality of life overall.

The problem, according to the authors, is that the etiology of widespread pain is poorly understood, and it is unclear whether it's the severity of knee pain or the structural damage associated with knee OA, or the combination of the two, that leads to widespread pain. And the answer to that is valuable because it can lead to more targeted interventions for pain management that can inhibit the development of widespread pain, they added.

The Multicenter Osteoarthritis Study is a longitudinal cohort of persons with at or at risk of knee OA. Participants in this study were characterized according to consistent frequent knee pain (CFKP), radiographic osteoarthritis (ROA), symptomatic knee osteoarthritis (SxOA), and knee pain severity after 60 months (baseline for this study).

The authors wanted to determine the relationship of CFKP, ROA, SxOA and knee pain severity to the risk of developing incident widespread pain, defined as the presence of widespread pain at 84 months among those who didn't meet widespread pain criteria at 60 months.

Widespread pain was defined as "pain above and below the waist, on both sides of the body and axially, using a standard homunculus, excluding knee pain."

The researchers also identified, and adjusted for, other possible risk factors for widespread pain identified in the medical literature, such as comorbidities, depressive symptoms, pain catastrophizing, pain severity, physical activity, sleep, and fatigue.

"These findings demonstrate that a localized pain condition, such as knee OA, is a risk factor for the later development of WSP," they wrote.

Of the four phenotypes -- CFKP, ROA, SxOA, and knee pain severity regardless of structural damage -- only knee pain severity was significantly associated with widespread pain, to the extent that each point higher on the 0 to 20 WOMAC pain scale was associated with a 14% increased risk of incident widespread pain (adjusted odds ratio per subscale unit increase 1.11, 95% CI 1.05-1.17, P<0.001, crude OR 1.14).

Neither CFKP, ROA, nor SxOA -- independent of pain severity -- was significantly associated with the development of widespread pain. This suggested that "it is pain severity itself" that is the most important factor in the later development of widespread pain in persons with knee OA.

When the authors removed the adjustment of pain severity from their models, they did find significant associations with widespread pain for bilateral CFKP, SxOA and CFKP in either knee "suggesting that the symptoms in these phenotypes contribute to the risk of WSP in relation to their associated pain severity."

"These findings highlight the importance of pain symptomology as an important factor that can contribute to the onset of WSP, suggesting a possible role for sensitization and the importance of adequately managing pain symptoms," they concluded, adding that their findings also "support the need to further explore mechanism-based management of pain as a disease unto itself to avoid negative consequences of pain remaining untreated."

Among the limitations to the study was the fact the authors weren't able to adjust their analysis for all risk factors, such as cognitive decline, that have been reported in the medical literature.

Furthermore, the authors wrote that prospective studies have shown that the course of widespread pain can fluctuate over the course of several years in patients, making the true incidence of widespread pain difficult to discern. The authors also acknowledged that their 2-year time frame for follow-up may not be enough to detect widespread pain in some patients.

The Multicenter Osteoarthritis Study is supported by the NIH.

Carlesso disclosed support from the Canadian Institutes of Health Research, and OARSI. One co-author disclosed support from the NIH.

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